The present invention relates to semiconductor wafers, and, in particular, relates to the machines used in preparing wafers from the semiconductor material.
One device for cutting wafers from crystals is an edge mounted rotating metallic disk with a diamond impregnated surface on the inner diameter. The thickness of the disks on the inner diameter of the saw are typically 0.008 to 0.010 inches and they are rotating at very high speeds such as 5,000 rpm. The crystal is mounted firmly into moving assembly and processed into the moving disk. One wafer is sawn at a time at a speed of about one inch per minute. One of the disadvantages of this technique is that the high speed wheel has resonant vibrational modes that cannot be damped. This motion, combined with the irregularity of the diamond grit that rips its way through the brittle semiconductor material can impart an unacceptably high level of fracture damage into the materials such as GaAs, InP and CdTe.
The use of multiple wire cutting devices is well known in the art. For example, U.S. Pat. No. 4,574,769 discloses a multiple wire cutting device having a continuous wire wrapped multiple times around four blocks. A cutting material is applied to the wires in contact with the material to be cut. Clearly, if the wire broke, the whole crystal would be spoiled.
U.S. Pat. No. 4,646,710 discloses a multiple wire cutting device wherein a multiple of independently mounted, parallel wires are placed upon a material mounted to a rocker. The wires move as well as the rocker.
U.S. Pat. No. 4,655,191 discloses a source of multiple wires that are used to cut a material. As the wire is worn out, a wire supply moves the wires so that another used area is used for the cutting action.
U.S. Pat. No. 4,903,682 discloses a multiple wire cutting apparatus that has a single wire feed which allows multiple parallel wires to be positioned in the cutting area.